1. Field of the Invention
The invention relates to an image processing method of an image processing apparatus for correcting an image, the image processing apparatus, and an image forming apparatus having an image correcting function.
2. Related Background Art
An image forming apparatus such as printer, copying apparatus, or the like forms an image onto a medium on the basis of image information which is obtained. As an image which is formed, particularly, it is demanded that its concentration and color are reproduced with fidelity on the basis of the image information. However, there is such a problem that reproducibility deteriorates due to an aging change or the like in the image forming function of the image processing apparatus. To solve such a problem, the image information is corrected.
For example, a technique in which concentration of a predetermined concentration pattern is measured by an optical sensor and a concentration change is corrected on the basis of a concentration value obtained by the measurement has been disclosed in JP-A-2001-186350.
In the case where the optical sensor for the concentration correction is, for example, a reflecting type, if noises are included in the measurement result due to a deterioration in light source necessary for reflection, a change in measuring characteristics of the optical sensor, a change in distance to the concentration pattern, or the like or noises generated by some cause are included in the measurement result, noises called color noises having a deviation in a noise energy in frequency components are included when they are expressed by a graph in which the frequency components of the noises are shown on an axis of abscissa and energy components of the noises are shown on an axis of ordinate.
In the color noises, the deviation exists in the noise energy in the frequency components as compared with noises called white noises having characteristics in which a noise energy in the frequency components is flat. Therefore, an influence of the white noises in which the noise energy in the frequency components is flat can be relatively easily reduced because of the uniform characteristics. In the color noises, however, since the deviation exists in the noise energy in the frequency components, it is fairly difficult to reduce its influence and it is demanded to develop a correcting method in which the influence of the color noises is reduced.